1. Field of the Invention
The present invention relates to a hard multilayer film formed body which has a diamondlike carbon film on the outermost layer side, and a method for producing the same. The diamondlike carbon hard multilayer film formed body according to the present invention is suitably used for a surface protective film for a member which especially requires wear resistance in automobile parts, machine parts, precision tools, cutting tools, because it exhibits excellent adhesiveness to a substrate.
2. Description of the Related Art
Diamondlike carbon (hereinafter referred to as “DLC”) is amorphous carbon having intermediate properties between diamond and graphite, and called hard carbon, hard amorphous carbon, amorphous carbon, delmorphous carbon, i-carbon, diamond-shape carbon or the like. The DLC is used, for example, as a protective film for a member which requires wear resistance because of high hardness as well as diamond and excellent characteristics of wear resistance, solid lubricity, thermal conductivity and chemical stability.
Physical vapor deposition (PVD) such as sputtering or ion plating, and chemical vapor deposition (CVD) are adapted as a method for forming a DLC film. Particularly, a DLC film formed by cathode discharge type arc ion plating (hereinafter referred to as AIP) which uses solid carbon as an evaporation source (carbon target) is applied to the field of cutting tools and the like which especially require wear resistance, because it contains no hydrogen and can have high hardness close to diamond, compared with a DLC film formed by CVD. However, a DLC film with high hardness has an extremely large internal stress, and its deformability is extremely small. Therefore, it has a disadvantage of easily separating with low adhesiveness to the substrate. Therefore, it has been proposed for improving the adhesiveness to the substrate to extremely minimize the thickness of the DLC film with high hardness to about 0.1 μm.
The present inventors disclose Japanese Patent Laid-Open No. 2000-87218 as a method for improving the adhesiveness of DLC film formed by AIP, wherein a DLC film is formed on a surface of a metallic or ceramic substrate by cathode discharge type ion plating using a carbon target, and a mixed layer 10 to 500 Å in thickness composed of the substrate constituting elements and the film constituting elements is formed in the interface between the DLC film and the substrate. The mixed layer is formed by controlling application voltage to −400 to −5000V and vacuum degree to not more than 10 mTorr in DLC film formation, whereby the mixing effect of carbon (C) ion that is the DLC film forming material is enhanced. The adhesiveness to DLC film can be further enhanced by forming an intermediate layer 10 to 1000 Å in thickness comprising at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Si and Al between the substrate and the DLC film, and forming a mixed layer 10 to 500 Å in thickness comprising these intermediate layer constituting elements and the DLC film constituting elements in the interface between the intermediate layer and the DLC film. Therefore, according to the above-mentioned method, a DLC hard film formed body (which may be hereinafter called DLC formed body) having a high-hardness DLC film formed with good adhesiveness can be obtained.
However, in this method, since the mixing effect of C is used for forming the mixed layer as described above, the thickness of the mixed layer is limited to a narrow range from about 10 to 500 Å. Therefore, a hardness difference is caused between the substrate and the DLC film (in a case having no intermediate layer) or between the intermediate layer and the DLC film (in a case having the intermediate layer), which are arranged through such a thin mixed layer. When the substrate is composed of a material with relatively high hardness such as cemented carbide material or ceramics, satisfactory adhesiveness can be exhibited because the hardness difference is relatively small. However, when the substrate is composed of a material with relatively low hardness such as an iron-based substrate, which is generally used for mechanical parts, easy separation of DLC film becomes problematic. When the thickness of a multilayer film containing DLC film on the outermost surface side (a multilayer film including the intermediate layer and the DLC film, which may be hereinafter called DLC multilayer film) is as thick as not less than about 3 μm, this problem becomes noticeable because the whole stress of the DLC multilayer film is increased.
On the other hand, the present inventors disclose DLC hard multilayer film formed bodies comprising a predetermined intermediate layer between the substrate and the DLC film, which are formed using unbalanced magnetron sputtering (which may be hereinafter called UBM sputtering or UBMS) (Japanese Patent Laid-Open (JP) No. 2000-119843, U.S. Pat. No. 6,716,540, and Japanese Patent Laid-Open (JP) No. 2003-171758). The UBM sputtering forms an intermediate layer which can exhibit excellent adhesiveness to both the substrate and the DLC film, in addition to formation of a compact DLC film with high hardness.
General sputtering and UBM sputtering will be comparatively described in reference to FIGS. 3 and 4.
FIG. 3 is a schematic view showing a cathode structure for general sputtering. In the general sputtering, as shown in FIG. 3, ferrite magnets having the same magnetic property are disposed at the center and periphery of a circular target to form closed loops of magnetic lines of force in the vicinity of the target material. When a bias voltage is applied to a substrate, the substance constituting the target material is formed on the substrate. Although FIG. 4 shows an example using ferrite magnet, Sm-based rare earth magnet or Nd-based rare earth magnet can be used.
In the UBM sputtering, as shown in FIG. 4, magnets having different magnetic properties (ferrite magnet for the center and SmCo magnets for the periphery in FIG. 4) are disposed at the center part and periphery of a circular target, respectively. By disposing the different magnets in this way, a part of magnetic lines of force generated from the stronger magnet reaches as far as the vicinity of the substrate. As a result, plasma generated from sputtering along the magnetic lines of force (e.g., Ar plasma) is diffused as far as the vicinity of the substrate. According to the UBM sputtering, more Ar ions and electrons than those in general sputtering reach the substrate along the above-mentioned magnetic lines of force reaching as far as the vicinity of the substrate (ion-assist effect). Thus, the UBM sputtering can form a compact DLC film with high hardness. It further can form a homogeneous amorphous layer.
In the three related arts described above, as the intermediate layer to be arranged between the substrate and the DLC film, an intermediate layer of two-layer structure composed of, in order from the substrate side, a predetermined metal or a WC compound excellent in adhesiveness to the substrate and an amorphous containing this metal or WC compound and carbon (C) (JP No. 2000-119843 and U.S. Pat. No. 6,716,540) and an intermediate layer of four-layer structure (JP No. 2003-171758) using UBM sputtering are disclosed. JP No. 2000-119843, U.S. Pat. No. 6,716,540 and JP No. 2003-171758 are differed in the kind of substrates and in the structure of intermediate layer.
Specifically, JP No. 2000-119843 describes an intermediate layer of two-layer structure provided between a substrate such as an insulating material such as cemented carbide, Si or Al2O3 and a DLC film, the intermediate layer being composed of in order from the substrate side, a metal layer (first layer) comprising at least one metal selected from the group consisting of W, Ta, Mo and Nb and an amorphous layer (second layer) containing at least one of the metals described above and carbon.
U.S. Pat. No. 6,716,540 and JP No. 2003-171758 were made from the viewpoint of providing a DLC formed body capable of covering DLC film with good adhesiveness even in use of iron-based substrate. U.S. Pat. No. 6,716,540 describes an intermediate layer of two-layer structure composed of, in order from the substrate side, a metal layer (first layer) of Cr and/or Al and an amorphous layer (second layer) containing at least one of the above-mentioned metals and carbon. JP No. 2003-171758 discloses a first intermediate layer composed of, in order from the substrate side, a metal layer (first layer) of Cr and/or Al, a mixed layer (second layer) of a metal of Cr and/or Al and at least one metal selected from the group consisting of W, Ta, Mo and Nb, a metal layer (third layer) of at least one metal selected from the group consisting of W, Ta, Mo and Nb, and an amorphous layer (fourth layer) containing at least one metal selected from the group consisting of W, Ta, Mo and Nb and carbon (C), and a second intermediate layer composed of, in order from the substrate side, a metal layer (first layer) of Cr and/or Al, a mixed layer (second layer) of a metal of Cr and/or Al and a compound mainly composed of WC, a compound layer (third layer) mainly composed of WC, and an amorphous layer (fourth layer) containing a compound mainly composed of WC and carbon (C). The DLC formed body described in U.S. Pat. No. 6,716,540 is excellent in adhesiveness to, particularly, an iron-based substrate with relatively high hardness such as high speed tool steel (HSS), while the DLC formed body described in JP No. 2003-171758 is excellent in adhesiveness to, particularly, an iron-based substrate with relatively low hardness such as bearing steel, stainless steel or carbon steel.
According to the methods described in JP No. 2000-119843, U.S. Pat. No. 6,716,540 and JP No. 2003-171758, since an adequate intermediate layer is arranged in accordance with the kind of substrate, a DLC formed body capable of exhibiting excellent adhesiveness to both the substrate and the DLC film can be obtained even if a relatively thick DLC multilayer film is formed.
However, it is principally difficult for the sputtering including UBM sputtering to form a DLC film with extremely high hardness as in the AIP which uses carbon ion as a raw material. Therefore, the DLC film formed using the sputtering is inferior in wear resistance to the DLC film formed using AIP.